The welcome message is just a function of the header block. Lesti_Fpc needs the welcome message in a seperated
block. In Magento 1.8 this is solved and the name of the block is welcome. In Magento 1.7 there is
a semi-solution in core, we just have to give a little help.

Were to find Welcome Message Block in Magento 1.7

The welcome message block in Magento 1.7 exists, but it isn't used. You can find the block under
app/code/core/Mage/Page/Block/Html/Welcome.php. In Magento 1.8 this block has the full functionallity for
the welcome message, but in Magento 1.7 the block just repeats the function of the header.

<?php
/**
* Magento
*
* NOTICE OF LICENSE
*
* This source file is subject to the Open Software License (OSL 3.0)
* that is bundled with this package in the file LICENSE.txt.
* It is also available through the world-wide-web at this URL:
* http://opensource.org/licenses/osl-3.0.php
* If you did not receive a copy of the license and are unable to
* obtain it through the world-wide-web, please send an email
* to license@magentocommerce.com so we can send you a copy immediately.
*
* DISCLAIMER
*
* Do not edit or add to this file if you wish to upgrade Magento to newer
* versions in the future. If you wish to customize Magento for your
* needs please refer to http://www.magentocommerce.com for more information.
*
* @category Mage
* @package Mage_Page
* @copyright Copyright (c) 2012 Magento Inc. (http://www.magentocommerce.com)
* @license http://opensource.org/licenses/osl-3.0.php Open Software License (OSL 3.0)
*/
/**
* Html page block
*
* @category Mage
* @package Mage_Page
* @author Magento Core Team <core@magentocommerce.com>
*/
class Mage_Page_Block_Html_Welcome extends Mage_Core_Block_Template
{
/**
* Get block messsage
*
* @return string
*/
protected function _toHtml()
{
return Mage::app()->getLayout()->getBlock('header')->getWelcome();
}
}

Why we can't use this welcome block?

That isn't good for Fpc. Cause the Fpc builds a minimal layout for the dynmaic and lazy blocks before it replaces
the placeholders and sends response to the customer. And the Fpc just takes the dynamic and lazy blocks in this
layout to reduce the time to build layout. But if the welcome block needs the header block to get the welcome
message the layout can't give the header block. So we have to build the welcome block like Magento 1.8 does. The
easiest way is just to copy the source from Magento 1.8 and to copy it into community-pool
(not the recommended way). The source of
app/code/community/Mage/Page/Block/Html/Welcome.php.